There has been a need for an improved method of sensing the level of liquids, such as water, to sound an audible alarm in the presence of high water to prevent water damage. High water detection and alarm systems have been in use for some time.
One of the more common systems consists of a buoyant float that activates a switch closure to complete an electrical circuit, sounding an alarming device. These systems can be subject to various failures as the system ages and these failures may defeat the purpose of the alarm system; floats may develop pin holes and fill with water. Other possible modes of failure may include buoyant materials that eventually become saturated with the liquid and lose their buoyancy; pivots and other members that are subject to corrosion may stick, preventing reliable operation; switch contacts may oxidize, causing the alarm system to fail and not issue its warning.
Another type of level sensing system determines the fluid level by measuring the conductivity of water when its metallic electrodes are immersed in the water. In this type of system the electrodes are made of similar metals.
In 1883 Michael Faraday observed that pure water was an almost perfect insulator; whereas aqueous solutions of certain substances were electrically conductive. If two electrodes are dipped into a container of distilled water, and one electrode is connected to the positive terminal of a DC source, the other to the negative, practically no current flows. When a small amount acid, base or salt is added to the water, it provides, when dissolved in water, a solution whose resistance is sufficiently low for the current to be appreciable. A solution that conducts an electric current is called an electrolyte and this conduction phenomenon is more commonly known as electrolysis. The resistance of the solution depends markedly on the concentration and upon the temperature.
This system has the disadvantage of becoming unreliable when the probes oxidize over a period of time. If the process of oxidation occurs, the total measured resistance will increase dramatically.
Other liquid level sensing systems sense the change in capacitance within a vessel to determine the level of the fluid. These systems are rather insensitive because small changes in the height of the fluid are not easily or reliably determined from the very small changes in capacitance.
Another system of sensing the fluid level is by determining the change of resistance when a self heated thermistor is immersed into the liquid. A self heated thermistor has the disadvantage of being unreliable when cooled to much and tripping the alarm if the ambient temperature suddenly drops. Wind passing by an unprotected thermistor can also give a false nuisance alarm. Generally, this system is more costly to produce.
Radon-222 was first discovered in 1900 by the German chemist Friedrich Ernst Dorn. It is a dense, colorless, radioactive, inert gaseous element formed by the radioactive decay of radium. Its most stable isotope is Rn 222 having a half-life of 3.82 days, decaying by the emission of alpha particles into an isotope of the element polonium. Small quantities, formed by the decay of uranium minerals, are found in rock and soil, and radon makes up most normal background radioactivity.
Radon is naturally produced by the radioactive decay of uranium-238 that is present in soil and in rock formations. Radon is found in homes and other buildings that were built on black shale or uranium bearing soil. In these areas, an open sump well allows radon gas to enter into a dwelling.
There are several patents that disclose water level sensing and alarm systems.
U.S. Pat. No. 4,369,438, granted Jan. 18, 1983, to J. R. Wilhelmi discloses a sump pump detection and alarm system that generates an alarm in the event (1) high water is detected with power available, (2) high water is detected in the absence of power, or (3) when there is a power failure to the pump at any time.
U.S. Pat. No. 4,456,432, granted Mar. 1, 1984, to V. Mannino, discloses an emergency sump pump and alarm warning system comprised of an auxiliary battery powered sump pump that emits an intermittent audible and visual alarm when the battery powered sump pump is activated.
U.S. Pat. No. 4,841,282, granted Jun. 20, 1989, to G. A. Reis, discloses a liquid level detector for use in sump wells with a prior art smoke alarm of the ionization type contained in an electrically conductive housing and responsive to the pressure of a predetermined ionization level therein.
U.S. Pat. No. 5,314,313, granted May 24, 1994, to L. Janesky discloses an alarm system that sounds an audible alarm whenever the water level within a sump pump enclosure exceeds the operating level of the sump pump.
Therefore, it can be concluded that there exists a continuing need for the development of reliable and safe detection devices that can detect the presence of high water and the undesirable presence of radon gas. In this regard, this invention fulfills this need.